By the rivers of Babylon, there we sat down, yea, we wept, when we remembered Zion.
Sat — The usual posture of mourners.
 We hanged our harps upon the willows in the midst thereof.
Harps — Harps are here put for all instruments of musick.
 For there they that carried us away captive required of us a song; and they that wasted us required of us mirth, saying, Sing us one of the songs of Zion.
A song — Such songs as you used to sing in the temple of Zion.
 How shall we sing the LORD's song in a strange land?
The Lord's — Those songs which were appointed by God to be sung only in his service.
 If I do not remember thee, let my tongue cleave to the roof of my mouth; if I prefer not Jerusalem above my chief joy.
If — If I do not value Jerusalem's prosperity more than all other delights.
 Remember, O LORD, the children of Edom in the day of Jerusalem; who said, Rase it, rase it, even to the foundation thereof.
The day — In the time of its destruction.
 O daughter of Babylon, who art to be destroyed; happy shall he be, that rewardeth thee as thou hast served us.
Happy — As being God's instrument to vindicate his honour, and execute his just judgments.